1. Field of the Invention
The present invention relates to a substrate supporting mechanism including a function for heating a substrate, such as a semiconductor wafer, placed thereon in a process container of a substrate processing apparatus, such as a film formation apparatus. The present invention further relates to a substrate processing apparatus including the substrate supporting mechanism.
2. Description of the Related Art
In order to manufacture semiconductor devices, vacuum processes, such as a CVD film formation process, an oxidation process, and a nitridation process, are performed on a semiconductor wafer (which will be simply referred to as “wafer”, hereinafter) treated as a target substrate. Where a process of this kind is performed as a single-substrate process, a substrate processing apparatus used for this purpose is provided with a substrate worktable disposed in a vacuum-sustainable chamber to place thereon a target substrate or wafer. The substrate worktable includes a heating mechanism to heat the target substrate or wafer to a predetermined temperature during the process.
As a substrate worktable including such a heating mechanism, there is proposed a ceramic heater that is high in resistance against corrosive gases and is also high in thermal efficiency (Jpn. Pat. Appln. KOKAI Publication No. 7-272834 and so forth). This ceramic heater includes a base body formed of an aluminum nitride sintered body and serving as a worktable for placing a target substrate thereon. The base body is provided with a heating element built therein and made of a refractory metal.
However, in recent years, it is required to perform a plasma process while maintaining a target substrate, such as a semiconductor wafer, at a very high temperature of about 800° C. Under such harsh conditions, the ceramic heater described above is unusable, because the aluminum nitride sintered body suffers physical damage and/or dielectric breakdown due to thermal distortion.
As a substrate worktable usable under a high temperature as described above, there is known a structure that includes a quartz base having an inner bore and a heating element formed of a silicon carbide sintered body and disposed in the inner bore (Jpn. Pat. Appln. KOKAI Publication No. 2005-302936). This structure can heat a target substrate to a high temperature of about 800° C. without causing the problem described above.
However, in order to attain such a high temperature, the heating element requires a very large electric current to be supplied. Further, the heating element is present in a chamber set in a vacuum state, and is densely disposed to have portions adjacent to each other in order to attain high process uniformity. Consequently, a problem arises such that electric discharge is easily caused by an electric field generated in a space containing the heating element. If electric discharge occurs on the heating element, it becomes difficult to stably perform a process. Further, particles may be generated and bring about contamination, by which it becomes difficult to perform the process in a clean state.